The hard disk drive is usually used as a binary information storage device, which consists of rapidly rotating disk with a magnetic surface and write-and-read head(s). The writing head creates strong magnetic fields and orients the magnetic particles on the surface of the disk. Switching the direction of the magnetic field yields a transition between the uniformly magnetized regions on the magnetic surface. This transition is detected as a binary 1 by a reading sensor. The absence of a transition at the measurement time is set to 0.
Our invention gives a practical new feature for the hard disk drive. It can work as an elementary processor (a logic device used to process binary information). Logic operations on the hard disk drive can be used as both a supplemental tool for a conventional semiconductor processor and for independent data processing. The Speed of this logic processor can be very high (˜108 bit/sec and more): it is defined by the number of revolutions per second (˜102 sec−1) multiplied by the bit length of the track (˜106 bit). The advantages include long binary word processing (important for a search of information) and small energy consumption which is mostly defined by a rotating motor.
The method of how to perform logic operations on a hard disk drive includes two important components. The first component is that the magnetic recording medium should be capable of superimposing the binary information. This make it possible to write two binary numbers sequentially on the same track while using different recording fields (strong and moderate ones), so that the resulting magnetization profile contains information about both written numbers. Three magnetization states (−M, 0, and +M) of the medium are utilized. Such a medium contains magnetic particles with 1) different anisotropy fields and/or with 2) different anisotropy axes orientations. For example, the first is an oriented (perpendicular or patterned) medium with a distribution of anisotropy fields. The second is typical for a longitudinal medium. One can also mention a so-called AFC medium, where a kind of magnetic superimposition was used to test the medium [E. E Fullerton et al., IEEE Trans. Magn. vol. 39, No. 2, p. 639 (2003)].
The second condition is, in order to perform logic operations, the binary information is encoded as 0−>00 and 1−>11. Technically this representation can be made with the doubling of the clock frequency for the hard disk drive.
The logic operation during disk revolutions includes three steps. In the beginning, strong magnetic fields created by the writing head record on a track the first binary number (A) as the sequence of transitions between different magnetization states (−M and +M). All previous information is erased. Then, moderate magnetic fields (from the same or other writing head), that can reverse just a part of magnetic particles, are applied to the same track and record on these particles the second binary number (B). Thus we obtain the superimposed transitions between 0 and M, −M and 0, and −M and M states. Finally, the reading sensor detects the magnetization transitions and gives the result of the logic operation for A and B.